As filed with the Securities and Exchange Commission on February 9, 2001

                                       Registration Statement No. 333-54648
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                ---------------

                            Amendment No. 1 to
                                    Form S-3
                             Registration Statement
                                     Under
                           the Securities Act of 1933
                                ---------------
                           American Tower Corporation
             (Exact name of registrant as specified in its charter)
                                ---------------
              Delaware                                 65-072387
  (State or other jurisdiction of         (I.R.S. Employer Identification No.)
   incorporation or organization)
                             116 Huntington Avenue
                          Boston, Massachusetts 02116
                                 (617) 375-7500
  (Address, including zip code, and telephone number, including area code, of
                   registrant's principal executive offices)
                                ---------------
                                Steven B. Dodge
                            Chief Executive Officer
                           American Tower Corporation
                             116 Huntington Avenue
                          Boston, Massachusetts 02116
                                 (617) 375-7500
 (Name, address, including zip code, and telephone number, including area code,
                             of agent for service)
                                ---------------
                                   Copies to:
                             David E. Redlick, Esq.
                           Matthew J. Gardella, Esq.
                               Hale and Dorr LLP
                                60 State Street
                          Boston, Massachusetts 02109
                           Telephone: (617) 526-6000
                            Telecopy: (617) 526-5000
   Approximate date of commencement of proposed sale to public: As soon as
practicable after this Registration Statement becomes effective.
   If the only securities being registered on this Form are being offered
pursuant to dividend or interest reinvestment plans, please check the following
box. [_]

   If any of the securities being registered on this Form are to be offered on
a delayed or continuous basis pursuant to Rule 415 under the Securities Act of
1933, other than securities offered only in connection with dividend or
interest reinvestment plans, check the following box. [X]
   If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following
box and list the Securities Act registration statement number of the earlier
effective registration statement for the same offering. 333-  . [_]
   If this Form is a post-effective amendment filed pursuant to Rule 462(c)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering. 333-  . [_]
   If delivery of the prospectus is expected to be made pursuant to Rule 434,
please check the following box. [_]
                                ---------------
                        CALCULATION OF REGISTRATION FEE

-----------------------------------------------------------------------------
-----------------------------------------------------------------------------

                                                      Proposed
                                         Proposed      Maximum
                           Amount        Maximum      Aggregate   Amount of
 Title of Shares to be      to be     Offering Price  Offering   Registration
      Registered        Registered(1)  Per Share(2)   Price(2)       Fee
-----------------------------------------------------------------------------
                                                     
Class A Common Stock,
 $.01 par value per
 share.................   1,134,735       $34.75     $39,432,041 $9,858.01(3)
-----------------------------------------------------------------------------
-----------------------------------------------------------------------------


(1) Pursuant to Rule 416 of the Securities Act, the amount to be registered in
    this Registration Statement shall also cover an indeterminate number of
    shares of Class A common stock issuable as a result of stock dividends,
    stock splits, recapitalizations or any other similar transactions effected
    without the receipt of consideration which results in an increase in the
    number oif the Registrant's outstanding shares of Class A common stock.

(2) Estimated solely for purposes of calculating the registration fee pursuant
    to Rule 457(c) under the Securities Act and based upon the average of the
    high and low prices on the New York Stock Exchange on February 5, 2001.

(3) The Registrant previously paid $9,944.61 in connection with the initial
    filing of this Registration Statement and therefore no additional filing is
    required herewith.

                                ---------------
   The Company hereby amends this Registration Statement on such date or dates
as may be necessary to delay its effective date until the Company shall file a
further amendment which specifically states that this Registration Statement
shall thereafter become effective in accordance with Section 8(a) of the
Securities Act of 1933 or until the Registration Statement shall become
effective on such date as the Commission, acting pursuant to said Section 8(a),
shall determine.
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------


++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+The information in this prospectus is not complete and may be changed. The    +
+selling stockholders named in this prospectus may not sell these securities   +
+until the registration statement filed with the Securities and Exchange       +
+Commission is effective. This prospectus is not an offer to sell these        +
+securities and the selling stockholders named in this prospectus are not      +
+soliciting offers to buy these securities in any jurisdiction where the offer +
+or sale is not permitted.                                                     +
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

               Subject to completion, dated February 9, 2001

PROSPECTUS

                 1,134,735 Shares of Class A Common Stock

                           American Tower Corporation

                                 ------------

  This prospectus relates to resales of shares of our Class A common stock
previously issued by us to the former stockholders of InterPacket Networks,
Inc. in connection with our acquisition of that company.

  We will not receive any proceeds from the sale of the shares.

  The selling stockholders identified in this prospectus, or their pledgees,
donees, transferees or other successors-in-interest, may offer the shares from
time to time through public or private transactions at prevailing market
prices, at prices related to prevailing market prices or at privately
negotiated prices.

  Holders of Class A common stock are entitled to one vote per share and
holders of Class B common stock to ten votes per share generally.

  Our Class A common stock is traded on the New York Stock Exchange under the
symbol "AMT." On February 5, 2001, the closing sale price of our Class A common
stock on the New York Stock Exchange was $35.08 per share. You are urged to
obtain current market quotations for our Class A common stock.

                                 ------------

  Investing in our Class A common stock involves a high degree of risk. See
"Risk Factors" beginning on page 2.

                                 ------------

  Neither the Securities and Exchange Commission nor any state securities
commission has approved or disapproved of these securities or determined if
this prospectus is truthful or complete. Any representation to the contrary is
a criminal offense.

                                 ------------

                  The date of this prospectus is       , 2001.


                               TABLE OF CONTENTS



                                                                            Page
                                                                            ----
                                                                         
RISK FACTORS...............................................................   2
CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS.......................   7
USE OF PROCEEDS............................................................   8
SELLING STOCKHOLDERS.......................................................   8
DESCRIPTION OF CAPITAL STOCK...............................................  11
PLAN OF DISTRIBUTION.......................................................  14
LEGAL MATTERS..............................................................  15
EXPERTS....................................................................  15
WHERE YOU CAN FIND MORE INFORMATION........................................  16
INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE............................  16


   We have not authorized anyone to provide you with information different from
that contained or incorporated by reference in this prospectus. The selling
stockholders are offering to sell, and seeking offers to buy, shares of our
Class A common stock only in jurisdictions where offers and sales are
permitted. The information contained in this prospectus is accurate only as of
the date of this prospectus, regardless of the time of delivery of this
prospectus or of any sale of Class A common stock.


                                 AMERICAN TOWER

   We are a leading wireless communications and broadcast infrastructure
company operating in three business segments.

  .  We operate the largest network of wireless communications towers in
     North America and are the largest independent operator of broadcast
     towers in North America, based on number of towers.

  .  We provide comprehensive network development services and components for
     wireless service providers and broadcasters.

  .  Through our Verestar subsidiary, we are a leading provider of integrated
     satellite and fiber network access services for telecommunications
     companies, Internet service providers, broadcasters and maritime
     customers, both domestic and international, based on number of teleport
     antennae and facilities.

   American Tower Corporation's executive offices are located at 116 Huntington
Avenue, Boston, Massachusetts 02116. Our telephone number is (617) 375-7500.
Unless the context otherwise requires, references in this prospectus to
"American Tower," "we," "us," and "our" refer to American Tower Corporation and
its subsidiaries.


                                  RISK FACTORS

   An investment in our Class A common stock involves a high degree of risk. If
any of the following events occurs, our business, financial condition and
results of operations would likely suffer, possibly materially.

Decrease in demand for tower space would materially and adversely affect our
cash flow and we cannot control that demand

   Many of the factors affecting the demand for tower space, and to a lesser
extent our services business, affect our cash flow. Those factors include:

  .  consumer demand for wireless services,

  .  the financial condition of wireless service providers and their
     preference for owning as opposed to leasing antenna sites,

  .  the growth rate of wireless communications or of a particular wireless
     segment,

  .  the number of wireless service providers in a particular segment,
     nationally or locally,

  .  governmental licensing of broadcast rights,

  .  increased use of roaming and resale arrangements by wireless service
     providers. These arrangements enable a provider to serve customers
     outside its license area, to give licensed providers the right to enter
     into arrangements to serve overlapping license areas and to permit
     nonlicensed providers to enter the wireless marketplace. Wireless
     service providers might consider such roaming and resale arrangements as
     superior to constructing their own facilities or leasing antenna space
     from us,

  .  zoning, environmental and other government regulations, and

  .  technological changes.

   The demand for antenna space is dependent, to a significantly lesser extent,
on the needs of television and radio broadcasters. Among other things, certain
technological advances, including the development of satellite-delivered radio,
may reduce the need for tower-based broadcast transmission. We could also be
affected adversely should the development of digital television be delayed or
impaired, or if demand for it were to be less than anticipated because of
delays, disappointing technical performance or cost to the consumer.

Our substantial leverage and debt service obligations may adversely affect our
cash flow and our ability to make payments on our senior notes

   We have a substantial amount of outstanding indebtedness. After giving
effect to our sale of 10.0 million shares of Class A common stock in January
2001, our sale of $1.0 billion of 9 3/8 % senior notes due 2009 in January 2001
and borrowings that we assume we would have made to close acquisitions that
were pending as of September 30, 2000, we would have had at September 30, 2000
approximately $3.4 billion of consolidated debt and a debt to equity ratio of
1.05 to 1. Our substantial level of indebtedness increases the possibility that
we may be unable to generate cash sufficient to pay when due the principal of,
interest on or other amounts due in respect of our indebtedness. We may also
obtain additional long-term debt and working capital lines of credit to meet
future financing needs. This would have the effect of increasing our total
leverage.

   Our substantial leverage could have significant negative consequences,
including:

  .  increasing our vulnerability to general adverse economic and industry
     conditions,

  .  limiting our ability to obtain additional financing,

  .  requiring the dedication of a substantial portion of our cash flow from
     operations to service our indebtedness, thereby reducing the amount of
     our cash flow available for other purposes, including capital
     expenditures,

  .  requiring us to sell debt or equity securities or to sell some of our
     core assets, possibly on unfavorable terms, to meet payment obligations,

                                       2


  .  limiting our flexibility in planning for, or reacting to, changes in our
     business and the industries in which we compete, and

  .  placing us at a possible competitive disadvantage with less leveraged
     competitors and competitors that may have better access to capital
     resources.

   A significant portion of our outstanding indebtedness bears interest at
floating rates. As a result, our interest payment obligations on such
indebtedness will increase if interest rates increase.

Restrictive covenants in our credit facilities and our senior notes could
adversely affect our business by limiting flexibility

   The indenture for our senior notes due 2009 and our credit facilities
contain restrictive covenants that limit our ability to take various actions
and engage in various types of transactions, including:

  .  paying dividends and making distributions or other restricted payments,

  .  incurring more debt, guaranteeing indebtedness and issuing preferred
     stock,

  .  issuing stock of certain subsidiaries,

  .  making certain investments,

  .  creating liens,

  .  entering into transactions with affiliates,

  .  entering into sale-leaseback transactions, and

  .  merging, consolidating or selling assets.

   These covenants could have an adverse effect on our business by limiting our
ability to take advantage of financing, merger and acquisition or other
corporate opportunities.

Build-to-suit construction projects and major acquisitions from wireless
service providers increase our dependence on a limited number of customers, the
loss of which could materially decrease revenues, and may also involve less
favorable terms

   Our increasing focus on major build-to-suit projects for wireless service
providers and related acquisitions entail several unique risks. First is our
greater dependence on a limited number of customers and the risk that customer
losses could materially decrease revenues. Another risk is that our agreements
with these wireless service providers have lease and control terms that are
more favorable to them than the terms we give our tenants generally. In
addition, although we have the benefit of an anchor tenant in build-to-suit
projects, we may not be able to find a sufficient number of additional tenants.
In fact, one reason wireless service providers may prefer build-to-suit
arrangements is to share or escape the costs of an undesirable site. A site may
be undesirable because it has high construction costs or may be considered a
poor location by other providers.

Our expanded construction program increases our exposure to risks that could
increase costs and adversely affect our earnings and growth

   Our expanded construction activities involve substantial risks. These risks
include:

  .  increasing our debt and the amount of payments on that debt,


  .  increasing competition for construction sites and experienced tower
     construction companies, resulting in significantly higher costs and
     failure to meet time schedules,

  .  failing to meet time schedules, which could result in our paying
     significant penalties to prospective tenants, particularly in build-to-
     suit situations, and

  .  possible lack of sufficient experienced personnel to manage an expanded
     construction program.

                                       3


   We cannot control the main factors that can prevent, delay or increase the
cost of tower construction. These factors include:

  .  zoning and local permitting requirements,

  .  environmental group opposition,

  .  availability of skilled construction personnel and construction
     equipment,

  .  adverse weather conditions, and

  .  federal regulations.

Increasing competition could make tower construction and acquisition more
costly

   Increased competition, which we believe will continue, has resulted in
substantially higher acquisition costs, particularly for towers being sold by
wireless service providers. That competition has also raised construction site
acquisition costs and created shortages for experienced tower construction
personnel. Because of personnel shortages, we could experience failures to meet
time schedules.

Increasing competition in the satellite and fiber network access services
market may slow Verestar's growth and adversely affect its business

   In the satellite and fiber network access services market, Verestar competes
with other satellite communications companies that provide similar services, as
well as other communications service providers. Some of Verestar's existing and
potential competitors consist of companies from whom Verestar currently leases
satellite and fiber network access in connection with the provision of
Verestar's services to its customers. Increased competition could result in
Verestar being forced to reduce the fees it charges for its services and may
limit Verestar's ability to obtain, on economical terms, services that are
critical to its business. We anticipate that Verestar's competitors may develop
or acquire services that provide functionality that is similar to that provided
by Verestar's services and that those competitive services may be offered at
significantly lower prices or bundled with other services. Many of the existing
and potential competitors have financial and other resources significantly
greater than those available to Verestar.

If we cannot keep raising capital, our growth will be impeded

   Without additional capital, we would need to curtail our acquisition and
construction programs which are essential for our long-term success. We expect
to use borrowed funds to satisfy a substantial portion of our capital needs.
However, we must continue to satisfy financial ratios and to comply with
financial and other covenants in order to do so. If our revenues and cash flow
do not meet expectations, we may lose our ability to borrow money or to do so
on terms we consider to be favorable. Conditions in the capital markets also
will affect our ability to borrow, as well as the terms of those borrowings.
All of these factors could also make it difficult or impossible for us
otherwise to raise capital.

If we cannot successfully integrate acquired sites or businesses or manage our
operations as we grow, our business will be adversely affected and our growth
may slow or stop

   A significant part of our growth strategy is the continued pursuit of
strategic acquisitions of independent tower operators and consolidators,
wireless service providers and service and teleport businesses. We cannot
assure you, however, that we will be able to integrate successfully acquired
businesses and assets into our existing business. Since January 1, 2000, we
have consummated more than 60 transactions involving the acquisition of more
than 4,740 communications sites and related businesses and several teleports
and related businesses. Our growth has placed, and will continue to place, a
significant strain on our management and operating and financial systems.
Successful integration of these and any future acquisitions will depend
primarily on our ability to manage these assets and combined operations and,
with respect to the services and teleport businesses, to integrate new
management and employees into our existing operations.

                                       4


If our chief executive officer left, we would be adversely affected because we
rely on his reputation and expertise, and because of our relatively small
senior management team

   The loss of our chief executive officer, Steven B. Dodge, has a greater
likelihood of having a material adverse effect upon us than it would on most
other companies of our size because of our comparatively smaller executive
group and our reliance on Mr. Dodge's expertise. Our growth strategy is highly
dependent on the efforts of Mr. Dodge. Our ability to raise capital also
depends significantly on the reputation of Mr. Dodge. You should be aware that
we have not entered into an employment agreement with Mr. Dodge. The tower
industry is relatively new and does not have a large group of seasoned
executives from which we could recruit a replacement for Mr. Dodge.

Expanding operations into foreign countries could create expropriation,
governmental regulation, funds inaccessibility, foreign exchange exposure and
management problems

   Our recent expansion into Canada and Mexico, and other possible foreign
operations in the future, could result in adverse financial consequences and
operational problems not experienced in the United States. We have made a
substantial loan to a Mexican company and are committed to construct a sizable
number of towers in that country. We have also invested in a Canadian joint
venture that intends to acquire and construct towers in that country. As a
result of recent acquisitions by Verestar, we have network operation centers in
Europe, Asia, South America and Africa. We may also engage in comparable
transactions in other countries in the future. Among the risks of foreign
operations are governmental expropriation and regulation, inability to
repatriate earnings or other funds, currency fluctuations, difficulty in
recruiting trained personnel, and language and cultural differences, all of
which could impair our ability to manage and control operations.

Pro forma financial information is based on estimates and assumptions and may
not be indicative of actual future results

   Our actual future results could vary materially and adversely from those
reflected in the pro forma financial information we have incorporated by
reference in this prospectus. That information is based upon a number of
assumptions we believe to be reasonable. However, our three most significant
acquisitions to date, the ALLTEL, AirTouch and AT&T transactions, do not
involve acquisitions of businesses. The towers involved in those acquisitions
were operated as part of the wireless service divisions of ALLTEL, AirTouch and
AT&T. Those companies did not maintain extensive separate financial records or
prepare financial statements for the operation of those towers. We have,
however, included certain revenue and expense data of those towers in the pro
forma information. In the case of certain expenses, we have estimated amounts
based on both the limited information furnished by the carriers and our own
experience with comparable towers. None of our auditors, ALLTEL's auditors,
AirTouch's auditors or AT&T's auditors has expressed any opinion or provided
any form of assurance with respect to ALLTEL's, AirTouch's or AT&T's historical
data presented in the unaudited pro forma financial information.

New technologies could make our tower antenna leasing services less desirable
to potential tenants and result in decreasing revenues

   The development and implementation of signal combining technologies, which
permit one antenna to service two different transmission frequencies and,
thereby, two customers, may reduce the need for tower-based broadcast
transmission and hence demand for our antenna space.

   Mobile satellite systems and other new technologies could compete with land-
based wireless communications systems, thereby reducing the demand for tower
lease space and other services we provide. The Federal Communications
Commission has granted license applications for several low-earth orbiting
satellite systems that are intended to provide mobile voice or data services.
In addition, the emergence of new technologies could reduce the need for tower-
based transmission and reception and have an adverse effect on our operations.
The growth in delivery of video services by direct broadcast satellites could
also adversely affect demand for our antenna space.

                                       5


We could have liability under environmental laws

   Under various federal, state and local environmental laws, we, as an owner,
lessee or operator of more than 13,500 real estate sites, may be liable for the
substantial costs of remediating soil and groundwater contaminated by hazardous
wastes. Some of these laws impose responsibility and liability on us even if we
did not cause the contamination or even know about it. Almost all of the towers
we own and operate, other than roof top towers, are located on parcels of land,
which could result in substantial environmental liability. Our liability often
will continue even if we sell or cease to lease or operate the property.

Our business is subject to government regulations and changes in current or
future laws or regulations could restrict our ability to operate our business
as we currently do

   We are subject to federal, state and local regulation of our business. Both
the FCC and the FAA regulate towers used for wireless communications and radio
and television antennae. In addition, the FCC separately regulates wireless
communication devices operating on towers and licenses and regulates television
and radio stations broadcasting from towers. Similar regulations exist in
Mexico, Canada and other foreign countries regarding wireless communications
and the operation of communications towers. Failure to comply with applicable
requirements may lead to monetary penalties and may require us to indemnify our
customers against any such failure to comply. New regulations may impose
additional costly burdens on us which may affect our revenues and cause delays
in our growth.

   In January 2001, the FCC concluded investigations of several operators of
communications towers, including us. The FCC sent us a Notice of Apparent
Liability for Forfeiture preliminarily determining that we had failed to file
certain informational forms, had failed to properly post certain information at
various tower sites and on one occasion had failed to properly light a tower.
The FCC has proposed a fine of $212,000 and intends to undertake an additional
review of our overall procedures for and degree of compliance with the FCC's
regulations. The proposed fine represents a significant increase from the
amount that otherwise might be imposed in similar situations because of the
number of violations and the FCC's negative perception of our compliance.
Depending on the outcome of the further investigation, the FCC could take
additional adverse action against us. We are conducting our own internal
investigation into our regulatory compliance policies. Additionally, we are, as
permitted by the FCC's regulations, preparing a response to the FCC notice and
we will otherwise cooperate with the FCC in any further investigation to
resolve these matters.

   The construction and reconstruction of a substantial number of antennae
needed to deliver digital television service to our customers may require state
and local regulatory approvals. The FCC has indicated that it may adopt
preemptive guidelines. If adopted, such regulations may be more or less
restrictive than existing state and local regulations and may increase our
construction costs.

   Local regulations can delay or prevent new tower construction or site
upgrade projects, thereby limiting our ability to respond to customer demand.
In addition, these regulations increase costs associated with new tower
construction. Existing regulatory policies may adversely affect the timing or
cost of new tower construction and additional regulations may be adopted which
increase delays or result in additional costs to us.

Our costs could increase and our revenues could decrease due to perceived
health risks from radio emissions, especially if these perceived risks are
substantiated

   Public perception of possible health risks associated with cellular and
other wireless communications media could slow the growth of wireless
companies, which could in turn slow our growth. In particular, negative public
perception of, and regulations regarding, these perceived health risks could
slow the market acceptance of wireless communications services.

                                       6


   If a connection between radio emissions and possible negative health
effects, including cancer, were established, our operations, costs and revenues
would be materially and adversely affected. We do not maintain any significant
insurance with respect to these matters.

Control by our principal stockholders could deter mergers where you could get
more than current market price for your stock

   Steven B. Dodge, together with his affiliates, owned approximately 27.0% of
our total voting power as of January 30, 2001. Control by Mr. Dodge and others
may discourage a merger or other takeover of our company in which holders of
common stock may be paid a premium for their shares over then-current market
prices. Mr. Dodge, together with a limited number of our directors, may be able
to control or block the vote on mergers and other matters submitted to the
common stockholders.

              CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

   We have made forward-looking statements in this prospectus and the documents
incorporated by reference into this prospectus. Forward-looking statements
include those regarding our goals, beliefs, plans or current expectations and
other statements regarding matters that are not historical facts. For example,
when we use words such as "project," "believe," "anticipate," "plan," "expect,"
"estimate," "intend," "should," "would," "could," or "may," or other words that
convey uncertainty of future events or outcome, we are making forward-looking
statements. Forward-looking statements include statements concerning:

  .  the outcome of our growth strategy,

  .  future results of operations,

  .  liquidity and capital expenditures,

  .  construction and acquisition activities,

  .  debt levels and the ability to obtain financing and make payments on our
     debt,

  .  regulatory developments and competitive conditions in the communications
     site and wireless carrier industries,

  .  projected growth of the wireless communications and wireless carrier
     industries,

  .  dependence on demand for satellites for Internet data transmission, and

  .  general economic conditions.

   Our forward-looking statements are subject to risks and uncertainties. You
should note that many important factors, some of which are discussed elsewhere
in this prospectus and in the documents we have incorporated by reference,
could affect us in the future and could cause our results to differ materially
from those expressed in our forward-looking statements. For a discussion of
some of these factors, please read carefully the information in this prospectus
under "Risk Factors." We do not undertake any obligation to update forward-
looking statements made by us.

                                       7


                                USE OF PROCEEDS

   We will not receive any proceeds from the sale of shares of Class A common
stock by the selling stockholders. The selling stockholders will pay any
underwriting discounts and commissions and expenses incurred by them for
brokerage, accounting, tax or legal services or any other expenses incurred by
them in disposing of the shares. We will bear all other costs, fees and
expenses incurred in effecting the registration of the shares covered by this
prospectus, including, without limitation, all registration and filing fees,
exchange listing fees and fees and expenses of our counsel and our accountants.

                              SELLING STOCKHOLDERS

   We issued the shares of Class A common stock covered by this prospectus in a
private placement in connection with our acquisition of InterPacket Networks in
December 2000. The following table sets forth, to our knowledge, certain
information about the selling stockholders as of December 31, 2000.

   For purposes of the following table, beneficial ownership is determined in
accordance with the rules of the SEC, and includes voting or investment power
with respect to shares. Shares of Class A common stock issuable under stock
options that are exercisable within 60 days after December 31, 2000 are deemed
outstanding for computing the percentage ownership of the person holding the
options but are not deemed outstanding for computing the percentage ownership
of any other person. Unless otherwise indicated below, to our knowledge, all
persons named in the table have sole voting and investment power with respect
to their shares of Class A common stock, except to the extent authority is
shared by spouses under applicable law. The inclusion of any shares in this
table does not constitute an admission of beneficial ownership by the persons
named below.



                                                                         Shares of
                               Shares of                           Class A Common Stock
                         Class A Common Stock                       to be Beneficially
                          Beneficially Owned                        Owned After Offering
                         Prior to Offering (1)    Number of Shares          (1)
                         ------------------------    of Class A    -------------------------
    Names of Selling                                Common Stock
      Stockholders        Number      Percentage   Being Offered    Number       Percentage
    ----------------     ----------- ------------ ---------------- ----------   ------------
                                                                 
Access Technology
 Partners, L.P..........      32,246           *       32,246                0              *
Access Technology
 Partners Brokers Fund
 L.P....................         645           *          645                0              *
Joseph T. Arsenio II....      16,103           *       16,103                0              *
Jeffrey Barbakow........      57,790           *       57,790                0              *
BayStar Capital, L.P....      20,154           *       20,154                0              *
BayStar International
 Ltd....................      20,154           *       20,154                0              *
David & Annika
 Bernstein..............       4,335           *        4,335                0              *
Stanley & Charlotte
 Bernstein..............         723           *          723                0              *
Stephen & Gayle
 Bernstein..............         578           *          578                0              *
CBK Investments, G.P....       2,890           *        2,890                0              *
Hector Chao.............         283           *          283                0              *
Liz Chow................         202           *          202                0              *
City National Bank,
 Trustee................         289           *          289                0              *
David Vaun Crumly.......       5,779           *        5,779                0              *
Crumly Family Partners
 Limited................       2,168           *        2,168                0              *
Richard d'Abo...........       1,445           *        1,445                0              *
Delaware Charter
 Guarantee & Trust Co.,
 Cust. Joseph T. Arsenio
 II.....................       3,160           *        3,160                0              *
Delaware Charter
 Guarantee & Trust Co.,
 Cust. Joseph T. Arsenio
 II, IRA................         508           *          508                0              *
Delaware Charter
 Guarantee & Trust Co.,
 Cust. Joseph T. Arsenio
 II, IRA Rollover.......         450           *          450                0              *
Delaware Charter
 Guarantee & Trust Co.,
 Cust. Meredith M.
 Arsenio, IRA SEP.......       2,312           *        2,312                0              *
Andrew & Donna Dietz....         723           *          723                0              *
Irene B. Dorsey.........          33           *           33                0              *
EarlMost Investments,
 L.P....................       5,543           *        5,543                0              *
Evergreen Trust, U/A/D
 6-12-90................       4,335           *        4,335                0              *
Bruce and Patricia
 Fisher.................         326           *          326                0              *
Jonathan Gans...........      47,563           *       47,563                0              *
Rock Steven Gnatovich...         131           *          131                0              *


                                       8




                                                                           Shares of
                               Shares of                             Class A Common Stock
                          Class A Common Stock                        to be Beneficially
                           Beneficially Owned                         Owned After Offering
                          Prior to Offering (1)     Number of Shares          (1)
                          -------------------------    of Class A    -------------------------
    Names of Selling                                  Common Stock
      Stockholders         Number      Percentage    Being Offered    Number       Percentage
    ----------------      ------------ ------------ ---------------- ----------   ------------
                                                                   
David Golden............         1,008           *        1,008                0              *
Howard Goldman..........            42           *           42                0              *
Gotel Investments Ltd...        55,692           *       55,692                0              *
Bruce J. Greenbaum &
 Teri Greenbaum,
 Trustees...............         2,890           *        2,890                0              *
Ruth Greenbaum & Monroe
 A. Greenbaum,
 Trustees...............           723           *          723                0              *
Scott D. & Susan B.
 Greenbaum..............           723           *          723                0              *
Eliezer A. Gurfel
 III(2).................         1,301           *        1,301                0              *
Barry L. Guterman and
 Sheryl L. Guterman, Co-
 Trustees...............           326           *          326                0              *
Ken Halloway(2).........         1,939           *        1,939                0              *
Hambrecht & Quist
 California.............         2,016           *        2,016                0              *
Hambrecht & Quist
 Employee Venture Fund
 L.P. II................         2,016           *        2,016                0              *
Terry Hanson(2).........            14           *           14                0              *
Peter Hartz, Trustee U/A
 dtd 9/20/90 by Hartz
 Revocable Trust........           723           *          723                0              *
Carl Hirsch.............         7,224           *        7,224                0              *
Colin Holland...........         4,713           *        4,713                0              *
Intel Corporation.......       161,227           *      161,227                0              *
Charles Isgar...........           651           *          651                0              *
Yolanta Jakubiec........            30           *           30                0              *
June Investments, LLC ..         1,445           *        1,445                0              *
Kinda Associates, a
 Massachusetts General
 Partnership............         2,890           *        2,890                0              *
James Kolsrud(2)........        41,170           *       41,170                0              *
James Kolsrud(2) &
 Sookhi Ro..............         3,251           *        3,251                0              *
Mike Labriola...........         3,370           *        3,370                0              *
Evelyn Lee..............            66           *           66                0              *
James and Linda Lippman
 1989 Trust.............         2,890           *        2,890                0              *
Max Loubiere............           578           *          578                0              *
Jon Mansey(2)...........           705           *          705                0              *
Steve Meepos............         2,890           *        2,890                0              *
Brett Messing...........        54,912           *       54,912                0              *
Brian Messing...........         1,431           *        1,431                0              *
Brian and Sandy
 Messing................            60           *           60                0              *
Debra Messing...........           716           *          716                0              *
Natalie Messing, UGMA,
 Brett Messing,
 Custodian..............           148           *          148                0              *
Samantha Messing, UGMA,
 Brett Messing,
 Custodian..............           148           *          148                0              *
Steven J. Miller(2).....           391           *          391                0              *
Carlos Moran(2).........            14           *           14                0              *
Chris Mulhern(2)........            28           *           28                0              *
Mia Mulhern.............            28           *           28                0              *
Tom Mulhern.............            28           *           28                0              *
Michael Nesmith.........           586           *          586                0              *
Newberg Family Trust....         2,857           *        2,857                0              *
Barry Newburger.........         2,890           *        2,890                0              *
Mira Nikolic............            15           *           15                0              *
Norman Pattiz, Trustee,
 Pattiz Family Trust....        28,895           *       28,895                0              *
Philip Michael Nunez &
 Debora Weston Nunez,
 Trustees...............            66           *           66                0              *
Alyssa Pearlstein, UGMA,
David Pearlstein,
Custodian...............             6           *            6                0              *
David and Gina
 Pearlstein.............            60           *           60                0              *
Nicole Pearlstein, UGMA,
 David Pearlstein,
 Custodian..............             6           *            6                0              *
Sonny Pearlstein........         1,445           *        1,445                0              *
Sonny and Marsha
 Pearlstein.............            60           *           60                0              *
Zachary Pearlstein,
 UGMA, David Pearlstein,
 Custodian..............             6           *            6                0              *
Jim Petit...............           807           *          807                0              *
Pequot Private Equity
 Fund...................       362,761           *      362,761                0              *
R&M InterPacket
 Investors, G.P.........        16,326           *       16,326                0              *
Bruce Raben.............         2,745           *        2,745                0              *


                                       9




                                                                          Shares of
                                Shares of                           Class A Common Stock
                          Class A Common Stock                       to be Beneficially
                           Beneficially Owned                        Owned After Offering
                          Prior to Offering (1)    Number of Shares          (1)
                          ------------------------    of Class A    -------------------------
    Names of Selling                                 Common Stock
      Stockholders         Number      Percentage   Being Offered    Number       Percentage
    ----------------      ----------- ------------ ---------------- ----------   ------------
                                                                  
Josh Rafner.............          283           *          283                0              *
Mitchell S. Rosenzweig..          289           *          289                0              *
Alan Rothenberg.........        1,951           *        1,951                0              *
Mark Rubin..............          131           *          131                0              *
Allen Sciarillo(2)......          651           *          651                0              *
Robert Schiowitz........          289           *          289                0              *
The Sear Family Trust...          723           *          723                0              *
Lorri Segaux............          867           *          867                0              *
Michael J. Shepard......          578           *          578                0              *
Steven & Janine
 Simenhoff..............        2,890           *        2,890                0              *
Julie Spira(2), Trustee,
 The Julie Spira Inter
 Vivos Trust dated
 June 22, 2000..........        8,325           *        8,325                0              *
Jeffrey Sudikoff........       46,835           *       46,835                0              *
Timothy F.
 Sylvester(2)...........        5,141           *        5,141                0              *
George & Lenore Travis..          723           *          723                0              *
Bruce Tyson, Trustee for
 Evergreen Trust, U/A/D
 6-12-90................          456           *          456                0              *
Juliana Long Tyson, UGMA
 Bruce Tyson,
 Custodian..............          261           *          261                0              *
VF Family Partnership...          261           *          261                0              *
Paul Vogel..............          586           *          586                0              *
Gary Vollen.............        1,198           *        1,198                0              *
W2 Ventures Partners,
 LLC....................          723           *          723                0              *
Alan E. & Stephanie C.
 Weston, Trustees.......          593           *          593                0              *
Craig E. Weston.........           66           *           66                0              *
Rodney & Judith
 Williams...............          723           *          723                0              *
William Wisniewski......          344           *          344                0              *
Bob Wotherspoon.........        2,168           *        2,168                0              *
John Yona(2)............           14           *           14                0              *
Loveday Ziluca..........          723           *          723                0              *
Kenneth H. Zimble.......        2,890           *        2,890                0              *
Lisa Zimble.............           28           *           28                0              *
Oliver Zimble, UGMA,
 Peter Zimble,
 Custodian..............           28           *           28                0              *
Patricia E. Cohen Zimble
 Trust..................        2,890           *        2,890                0              *
Peter Zimble............       40,263           *       40,263                0              *
Shari Zimble............           28           *           28                0              *

--------
 * Less than one percent.
(1) We do not know when or in what amounts a selling stockholder may offer
    shares for sale. The selling stockholders may not sell any or all of the
    shares offered by this prospectus. Because the selling stockholders may
    offer all or some of the shares pursuant to this offering, and because
    there are currently no agreements, arrangements or understandings with
    respect to the sale of any of the shares, we cannot estimate the number of
    the shares that will be held by the selling stockholders after completion
    of the offering. However, for purposes of this table, we have assumed that,
    after completion of the offering, none of the shares covered by this
    prospectus will be held by the selling stockholders.

(2) Employees or former employees of American Tower Corporation and/or
    InterPacket Networks.

   None of the selling stockholders has held any position or office with, or
has otherwise had a material relationship with, us or any of our subsidiaries
within the past three years, except that the selling stockholders indicated
have been employed by us and/or InterPacket Networks.

                                       10


                          DESCRIPTION OF CAPITAL STOCK

   The description below summarizes the more important terms of our capital
stock. Because this section is a summary, it does not describe every aspect of
our capital stock. This summary is subject to and qualified in its entirety by
reference to the provisions of our restated certificate of incorporation, as
amended, which we refer to as our charter. We have incorporated by reference a
copy of our charter as an exhibit to the registration statement of which this
prospectus is a part.

General

   Our authorized capital stock consists of 20,000,000 shares of preferred
stock, $.0l par value per share, 500,000,000 shares of Class A common stock,
$.0l par value per share, 50,000,000 shares of Class B common stock, $.0l par
value per share, and 10,000,000 shares of Class C common stock, $.0l par value
per share.

Preferred Stock

   Our board of directors will determine the designations, preferences,
limitations and relative rights of the 20,000,000 authorized and unissued
shares of preferred stock. These include:

  .  the distinctive designation of each series and the number of shares that
     will constitute the series,

  .  the voting rights, if any, of shares of the series,

  .  whether shares of the series will be entitled to receive dividends and,
     if so, the dividend rate on the shares of the series, any restriction,
     limitation or condition upon the payment of the dividends, whether
     dividends will be cumulative, and the dates on which dividends are
     payable,

  .  the prices at which, and the terms and conditions on which, the shares
     of the series may be redeemed, if the shares are redeemable,

  .  the purchase or sinking fund provisions, if any, for the purchase or
     redemption of shares of the series,

  .  any preferential amount payable upon shares of the series upon our
     liquidation or the distribution of our assets,

  .  the price or rates of conversion at which, and the terms and conditions
     on which the shares of the series may be converted into other
     securities, if the shares are convertible, and

  .  whether the series can be exchanged, at our option, into debt
     securities, and the terms and conditions of any permitted exchange.

   The issuance of preferred stock, or the issuance of rights to purchase
preferred stock, could discourage an unsolicited acquisition proposal. In
addition, the rights of holders of common stock will be subject to, and may be
adversely affected by, the rights of holders of any preferred stock that we may
issue in the future.

Common Stock

   Dividends. Holders of record of shares of common stock on the record date
fixed by our board of directors are entitled to receive dividends as declared
by our board of directors out of funds legally available for the purpose. No
dividends may be declared or paid in cash or property on any share of any class
of common stock, however, unless simultaneously the same dividend is declared
or paid on each share of the other classes of common stock. Dividends in the
form of shares of stock of any company, including our company or any of our
subsidiaries, are excepted from that requirement. Therefore, in the case of
stock dividends, the shares paid as the dividend may differ as to voting rights
to the extent that voting rights now differ among the different classes of
common stock. In the case of any dividend payable in shares of common stock,
holders of each class of common stock are entitled to receive the same
percentage dividend, payable in shares of that class, as the holders of each
other class. Dividends and other distributions on common stock are also subject
to the rights of holders of any series of preferred stock or debt that may be
outstanding from time to time.

                                       11



   Voting Rights. Holders of shares of Class A common stock and Class B common
stock have the exclusive voting rights and will vote as a single class on all
matters submitted to a vote of the stockholders. The foregoing is subject to
the requirements of Delaware corporate law, special provisions in our charter
governing election of directors, certain Class A common stock class voting
rights and the rights of holders of any series of preferred stock that may be
outstanding from time to time. Each share of Class A common stock is entitled
to one vote and each share of Class B common stock is entitled to ten votes.
The holders of the Class A common stock, voting as a separate class, have the
right to elect two directors. The holders of the Class A common stock and Class
B common stock, voting together as a single class, have the right to elect the
other directors. The Class C common stock is nonvoting except as otherwise
required by Delaware corporate law.

   Delaware corporate law requires the affirmative vote of the holders of a
majority of the outstanding shares of any class or series of common stock to
approve, among other things, an adverse change in the powers, preferences or
special rights of the shares of that class or series. Our charter requires the
affirmative vote of the holders of not less than 66 2/3% of the Class A common
stock and Class B common stock, voting as a single class, to amend most of the
provisions of the charter, including those relating to the provisions of the
various classes of common stock, an increase or decrease in the number of
authorized shares of Class A common stock, Class B common stock or Class C
common stock, indemnification of directors, exoneration of directors for
certain acts and the super-majority provision.

   The provisions of our charter:

  .  prohibit the acquisition by Steven B. Dodge and his controlled entities
     of more than 49.99% of the aggregate voting power of all shares of
     capital stock entitled to vote generally for the election of directors,
     less the voting power represented at the date of determination by the
     shares of Class B common stock acquired by Thomas H. Stoner, a director,
     and purchasers affiliated with him in the January 1998 private offering
     and owned by them or certain affiliates,

  .  prohibit future issuances of Class B common stock, except upon exercise
     of then outstanding options and pursuant to stock dividends or stock
     splits,

  .  limit transfers of Class B common stock to permitted transferees,

  .  provide for automatic conversion of the Class B common stock to Class A
     common stock if the aggregate voting power of Mr. Dodge, Mr. Stoner and
     their respective controlled entities falls below 21.3% of the aggregate
     voting power of all shares of capital stock, and

  .  require the holders of a majority of Class A common stock to approve
     adverse amendments to the powers, preferences or special rights of the
     Class A common stock.

   Mr. Dodge, together with his affiliates, owned approximately 27.0% of our
total voting power as of January 30, 2001.

   Conversion Provisions. Shares of Class B common stock and Class C common
stock are convertible, at any time at the option of the holder, on a share for
share basis into shares of Class A common stock. The present owner of Class C
common stock can convert that stock only upon the occurrence of various events
specified in our charter in which such conversion is permissible or with the
consent of our board of directors. Shares of Class B common stock automatically
convert into shares of Class A common stock upon any sale, transfer, assignment
or other disposition other than (a) to permitted transferees, or (b) pursuant
to pledges but not to the pledgee upon foreclosure. Permitted transferees
include certain family members and other holders of Class B common stock.

   Liquidation Rights. Upon our liquidation, dissolution or winding up the
holders of each class of common stock are entitled to share ratably in all
assets available for distribution after payment in full of creditors and
payment in full to holders of preferred stock then outstanding of any amount
required to be paid to them. However, if shares of stock or securities of any
company, including any of our subsidiaries, are distributed in

                                       12



connection with our liquidation, dissolution or winding up, the shares or
securities that we distribute to holders of the various classes of our common
stock may differ as to voting rights to the extent that voting rights now
differ among the different classes of common stock.

   Other Provisions. The holders of common stock have no preemptive,
subscription or redemption rights and are not entitled to the benefit of any
sinking fund. The shares of common stock presently outstanding are validly
issued, fully paid and nonassessable.

   In any merger, consolidation or business combination, the holders of each
class of common stock must receive the identical consideration to that received
by holders of each other class of common stock, except if shares of common
stock or common stock of any other company are distributed, in which case the
shares may differ as to voting rights to the same extent that voting rights
then differ among the different classes of common stock.

   No class of common stock may be subdivided, consolidated, reclassified or
otherwise changed unless, concurrently, the other classes of common stock are
subdivided, consolidated, reclassified or otherwise changed in the same
proportion and in the same manner.

   Our charter restricts transfers of shares of our capital stock to the extent
necessary to comply with the FCC's foreign ownership limitations.

Dividend Restrictions

   Our borrower subsidiaries are prohibited under the terms of their credit
facilities from paying cash dividends or making other distributions on, or
making redemptions, purchases or other acquisitions of, their capital stock or
other equity interests, including preferred stock, except that, beginning on
April 15, 2004, if no default exists or would be created thereby under the
credit facilities, our borrower subsidiaries may pay cash dividends or make
other distributions to the extent that restricted payments, as defined in the
credit facilities, do not exceed 50% of excess cash flow, as defined in the
credit facilities, for the preceding calendar year. The indenture for our 9
3/8% senior notes due 2009 imposes significant limitations on the payment of
dividends by us to our stockholders.

Delaware Business Combination Provisions

   We are subject to the provisions of Section 203 of the General Corporation
Law of Delaware. Section 203 prohibits a publicly held Delaware corporation
from engaging in a "business combination" with an "interested stockholder" for
a period of three years after the person became an interested stockholder,
unless the business combination or the transaction in which the stockholder
became an interested stockholder is approved in a prescribed manner. A
"business combination" includes mergers, asset sales and other transactions
resulting in a financial benefit to the interested stockholder. Subject to
certain exceptions, an "interested stockholder" is a person who, together with
affiliates and associates, owns, or within the prior three years did own, 15%
or more of the corporation's voting stock. These provisions do not apply to Mr.
Dodge because our board of directors approved the transaction pursuant to which
he became an interested stockholder.

Listing of Class A Common Stock

   Our Class A common stock is traded on the New York Stock Exchange under the
symbol "AMT."

Transfer Agent and Registrar

   The transfer agent and registrar for the Class A common stock is
Computershare Investor Services LLC, 2 North La Salle, 3rd Floor, Chicago,
Illinois 60602 (telephone number (312) 588-4991).

                                       13


                              PLAN OF DISTRIBUTION

   The selling stockholders may offer and sell the shares covered by this
prospectus from time to time. The term "selling stockholders" includes donees,
pledgees, transferees or other successors-in-interest selling shares received
after the date of this prospectus from a selling stockholder as a gift, pledge,
partnership distribution or other non-sale related transfer. The selling
stockholders will act independently of us in making decisions with respect to
the timing, manner and size of each sale. Such sales may be made on one or more
exchanges or in the over-the-counter market or otherwise, at prices and under
terms then prevailing or at prices related to the then current market price or
in negotiated transactions. The selling stockholders may sell their shares by
one or more of, or a combination of, the following methods:

  .  purchases by a broker-dealer as principal and resale by such broker-
     dealer for its own account pursuant to this prospectus;

  .  ordinary brokerage transactions and transactions in which the broker
     solicits purchasers;

  .  block trades in which the broker-dealer so engaged will attempt to sell
     the shares as agent but may position and resell a portion of the block
     as principal to facilitate the transaction;

  .  an over-the-counter distribution in accordance with the rules of the
     Nasdaq National Market;

  .  in privately negotiated transactions; and

  .  in options transactions.

   In addition, the selling stockholders may sell any shares that qualify for
sale pursuant to Rule 144 under Rule 144 rather than pursuant to this
prospectus.

   To the extent required, we may amend or supplement this prospectus from time
to time to describe a specific plan of distribution. In connection with
distributions of the shares or otherwise, the selling stockholders may enter
into hedging transactions with broker-dealers or other financial institutions.
In connection with such transactions, broker-dealers or other financial
institutions may engage in short sales of the Class A common stock in the
course of hedging the positions they assume with selling stockholders. The
selling stockholders may also sell the Class A common stock short and redeliver
the shares to close out such short positions. The selling stockholders may also
enter into option or other transactions with broker-dealers or other financial
institutions which require the delivery to such broker-dealer or other
financial institution of shares offered by this prospectus, which shares such
broker-dealer or other financial institution may resell pursuant to this
prospectus, as supplemented or amended to reflect such transaction. The selling
stockholders may also pledge shares to a broker-dealer or other financial
institution, and, upon a default, such broker-dealer or other financial
institution, may effect sales of the pledged shares pursuant to this
prospectus, as supplemented or amended to reflect such transaction.

   In effecting sales, broker-dealers or agents engaged by the selling
stockholders may arrange for other broker-dealers to participate. Broker-
dealers or agents may receive commissions, discounts or concessions from the
selling stockholders in amounts to be negotiated immediately prior to the sale.

   In offering the shares covered by this prospectus, the selling stockholders
and any broker-dealers who execute sales for the selling stockholders may be
treated as "underwriters" within the meaning of the Securities Act in
connection with such sales. Any profits realized by the selling stockholders
and the compensation of any broker-dealer may be treated as underwriting
discounts and commissions.

   In order to comply with the securities laws of certain states, the shares
must be sold in such jurisdictions only through registered or licensed brokers
or dealers. In addition, in certain states the shares may not be sold unless
they have been registered or qualified for sale in the applicable state or an
exemption from the registration or qualification requirement is available and
is complied with.

   We have advised the selling stockholders that the anti-manipulation rules of
Regulation M under the Exchange Act may apply to sales of shares in the market
and to the activities of the selling stockholders and

                                       14


their affiliates. In addition, we will make copies of this prospectus available
to the selling stockholders for the purpose of satisfying the prospectus
delivery requirements of the Securities Act, which may include delivery through
the facilities of the New York Stock Exchange pursuant to Rule 153 under the
Securities Act. The selling stockholders may indemnify any broker-dealer that
participates in transactions involving the sale of the shares against certain
liabilities, including liabilities arising under the Securities Act.

   At the time a particular offer of shares is made, if required, a prospectus
supplement will be distributed that will set forth the number of shares being
offered and the terms of the offering, including the name of any underwriter,
dealer or agent, the purchase price paid by any underwriter, any discount,
commission and other item constituting compensation, any discount, commission
or concession allowed or reallowed or paid to any dealer, and the proposed
selling price to the public.

   We have agreed to indemnify the selling stockholders against certain
liabilities, including certain liabilities under the Securities Act.

                                 LEGAL MATTERS

   The validity of the shares offered by this prospectus has been passed upon
by Hale and Dorr LLP. Partners of Hale and Dorr LLP hold options to purchase
7,200 shares of our Class A common stock at $18.75 per share and own 10,000
shares of our Class A common stock.

                                    EXPERTS

   The consolidated financial statements of American Tower Corporation
incorporated in this prospectus by reference from American Tower Corporation's
annual report on Form 10-K for the year ended December 31, 1999 have been
audited by Deloitte & Touche LLP, independent auditors, as stated in their
report, which is incorporated herein by reference, and has been so incorporated
in reliance upon the report of such firm given upon their authority as experts
in accounting and auditing.

   We are incorporating the following financial statements by reference in this
prospectus from our Form 8-K dated March 30, 2000:

  .  The consolidated financial statements of UNIsite, Inc. and subsidiaries
     as of December 31, 1999 and 1998 and for each of the years in the three
     year period ended December 31, 1999 have been incorporated by reference
     herein and in the registration statement in reliance upon the report of
     KPMG LLP, independent certified public accountants, incorporated by
     reference herein, and upon the authority of said firm as experts in
     accounting and auditing.

  .  The consolidated financial statements of ICG Satellite Services, Inc.
     and subsidiary as of November 30, 1999 and for the eleven months ended
     November 30, 1999 have been incorporated by reference herein and in the
     registration statement in reliance upon the report of KPMG LLP,
     independent certified public accountants, incorporated by reference
     herein, and upon the authority of said firm as experts in accounting and
     auditing.

                                       15


                      WHERE YOU CAN FIND MORE INFORMATION

   We file reports, proxy statements and other documents with the SEC. You may
read and copy any document we file at the SEC's public reference room at
Judiciary Plaza Building, 450 Fifth Street, N.W., Room 1024, Washington, D.C.
20549. You should call 1-800-SEC-0330 for more information on the public
reference room. Our SEC filings are also available to you on the SEC's Internet
site at http://www.sec.gov. In addition, these materials may be read at the
offices of the New York Stock Exchange, 20 Broad Street, New York, New York
10005.

   This prospectus is part of a registration statement that we filed with the
SEC. The registration statement contains more information than this prospectus
regarding us and our Class A common stock, including certain exhibits and
schedules. You can obtain a copy of the registration statement from the SEC at
the address listed above or from the SEC's Internet site.

                INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

   The SEC requires us to "incorporate" into this prospectus information that
we file with the SEC in other documents. This means that we can disclose
important information to you by referring to other documents that contain that
information. The information incorporated by reference is considered to be part
of this prospectus. Information contained in this prospectus and information
that we file with the SEC in the future and incorporate by reference in this
prospectus automatically updates and supersedes previously filed information.
We incorporate by reference the documents listed below and any future filings
we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange
Act, prior to the sale of all the shares covered by this prospectus.

     (1) Our Annual Report on Form 10-K for the year ended December 31, 1999;

     (2) Our Quarterly Reports on Form 10-Q for the quarters ended March 31,
  June 30 and September 30, 2000;

     (3) Our Current Reports on Form 8-K dated January 28, 2000, January 31,
  2000, February 9, 2000, February 24, 2000, March 14, 2000, March 30, 2000,
  April 13, 2000, May 15, 2000, May 23, 2000, June 12, 2000, June 23, 2000,
  June 29, 2000, July 28, 2000, August 1, 2000, August 14, 2000,
  September 11, 2000, October 30, 2000, November 3, 2000, November 13, 2000,
  December 15, 2000, December 20, 2000, January 17, 2001, January 19, January
  22, 2001, January 29, 2001 and February 1, 2001;

     (4) The description of our Class A common stock contained in our
  registration statement on Form 8-A (File No. 001-14195), filed on June 4,
  1998; and

     (5) All of our filings pursuant to the Exchange Act after the date of
  filing the initial registration statement and prior to effectiveness of the
  registration statement.

   You may request a copy of these documents, which will be provided to you at
no cost, by writing or telephoning us using the following contact information:

     American Tower Corporation
     116 Huntington Avenue
     Boston, Massachusetts 02116
     Attention: Director of Investor Relations
     Telephone: (617) 375-7500

                                       16


                                    PART II

                     INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14. Other Expenses of Issuance and Distribution.

   The following table sets forth the various expenses to be incurred in
connection with the sale and distribution of the securities being registered
hereby, all of which will be borne by the Registrant (except any underwriting
discounts and commissions and expenses incurred by the selling stockholders for
brokerage, accounting, tax or legal services or any other expenses incurred by
the selling stockholders in disposing of the shares). All amounts shown are
estimates except the Securities and Exchange Commission registration fee.


                                                                 
   Filing Fee--Securities and Exchange Commission.................. $  9,858.01
   Legal fees and expenses......................................... $ 30,000.00
   Accounting fees and expenses.................................... $ 30,000.00
   Miscellaneous expenses.......................................... $ 35,000.00
                                                                    -----------
     Total Expenses................................................ $104,858.01
                                                                    -----------


Item 15. Indemnification of Directors and Officers.

   Section 102 of the Delaware General Corporation Law allows a corporation to
eliminate the personal liability of directors of a corporation to the
corporation or its stockholders for monetary damages for a breach of fiduciary
duty as a director, except where the director breached his duty of loyalty,
failed to act in good faith, engaged in intentional misconduct or knowingly
violated a law, authorized the payment of a dividend or approved a stock
repurchase in violation of Delaware corporate law or obtained an improper
personal benefit. The Registrant has included such a provision in Article Sixth
of its restated certificate of incorporation.

   Section 145 of the General Corporation Law of Delaware provides that a
corporation has the power to indemnify a director, officer, employee or agent
of the corporation and certain other persons serving at the request of the
corporation in related capacities against amounts paid and expenses incurred in
connection with an action or proceeding to which he is or is threatened to be
made a party by reason of such position, if such person shall have acted in
good faith and in a manner he reasonably believed to be in or not opposed to
the best interests of the corporation, and, in any criminal proceeding, if such
person had no reasonable cause to believe his conduct was unlawful; provided
that, in the case of actions brought by or in the right of the corporation, no
indemnification shall be made with respect to any matter as to which such
person shall have been adjudged to be liable to the corporation unless and only
to the extent that the adjudicating court determines that such indemnification
is proper under the circumstances.

   Article XII of the Registrant's By-Laws provides that the Registrant shall
indemnify each person who is or was an officer or director of the Registrant to
the fullest extent permitted by Section 145 of the Delaware General Corporation
Law.

   The Registrant has purchased directors' and officers' liability insurance
which would indemnify its directors and officers against damages arising out of
certain kinds of claims which might be made against them based on their
negligent acts or omissions while acting in their capacity as such.

                                      II-1


Item 16. Exhibits



 Exhibit
 Number                               Description
 ------- ---------------------------------------------------------------------
      
    4.1   Restated Certificate of Incorporation, as amended, of the Company as
          filed with the Secretary of State of the State of Delaware on June
          4, 1999 (incorporated by reference to Exhibit 3(i) from the
          Registrant's Quarterly Report of Form 10-Q (File No. 001-14195)
          filed on August 16, 1999).
    4.2   By-laws, as amended, of the Registrant (incorporated by reference to
          Exhibit 3.2 from the Registrant's Registration Statement on Form S-3
          (File No. 333-37988) filed on May 26, 2000).
    5.1   Opinion of Hale and Dorr LLP.
  *23.1   Consent of Deloitte & Touche LLP.
  *23.2   Consent of KPMG LLP.
  *23.3   Consent of KPMG LLP.
   23.4   Consent of Hale and Dorr LLP, included in Exhibit 5.1 filed
          herewith.

--------

*  Previously filed.

Item 17. Undertakings.

   Item 512(a) of Regulation S-K. The undersigned Registrant hereby undertakes:

   (1) To file, during any period in which offers or sales are being made, a
post-effective amendment to this Registration Statement:

     (i) To include any prospectus required by Section 10(a)(3) of the
  Securities Act of 1933, as amended (the "Securities Act");

     (ii) To reflect in the prospectus any facts or events arising after the
  effective date of this Registration Statement (or the most recent post-
  effective amendment thereof) which, individually or in the aggregate,
  represent a fundamental change in the information set forth in this
  Registration Statement. Notwithstanding the foregoing, any increase or
  decrease in the volume of securities offered (if the total dollar value of
  securities offered would not exceed that which was registered) and any
  deviation from the low or high end of the estimated maximum offering range
  may be reflected in the form of prospectus filed with the Commission
  pursuant to Rule 424(b) if, in the aggregate, the changes in volume and
  price represent no more than 20 percent change in the maximum aggregate
  offering price set forth in the "Calculation of Registration Fee" table in
  the effective Registration Statement; and

     (iii) To include any material information with respect to the plan of
  distribution not previously disclosed in this Registration Statement or any
  material change to such information in this Registration Statement;

provided, however, that paragraphs (1)(i) and (1)(ii) do not apply if the
information required to be included is a post-effective amendment by those
paragraphs is contained in periodic reports filed with or furnished to the
Commission by the Registrant pursuant to Section 13 or Section 15(d) of the
Securities Exchange Act of 1934, as amended (the "Exchange Act"), that are
incorporated by reference in this Registration Statement.

   (2) That, for the purposes of determining any liability under the Securities
Act, each post-effective amendment shall be deemed to be a new registration
statement relating to the securities offered therein, and the offering of such
securities at the time shall be deemed to be the initial bona fide offering
thereof.

   (3) To remove from registration by means of a post-effective amendment any
of the securities being registered which remain unsold at the termination of
the offering.

   Item 512(b) of Regulation S-K. The Registrant hereby undertakes that, for
purposes of determining any liability under the Securities Act, each filing of
the Registrant's annual report pursuant to Section 13(a) or 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to

                                      II-2


Section 15(d) of the Exchange Act) that is incorporated by reference in this
Registration Statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

   Item 512(h) of Regulation S-K. Insofar as indemnification for liabilities
arising under the Securities Act may be permitted to directors, officers and
controlling persons of the Registrant pursuant to the indemnification
provisions described herein, or otherwise, the Registrant has been advised that
in the opinion of the Securities and Exchange Commission such indemnification
is against public policy as expressed in the Securities Act and is, therefore,
unenforceable. In the event that a claim for indemnification against such
liabilities (other than the payment by the Registrant of expenses incurred or
paid by a director, officer or controlling person of the Registrant in the
successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the
matter has been settled by controlling precedent, submit to a court of
appropriate jurisdiction the question whether such indemnification by it is
against public policy as expressed in the Securities Act and will be governed
by the final adjudication of such issue.

                                      II-3


                                   SIGNATURES

   Pursuant to the requirements of the Securities Act of 1933, as amended, the
Registrant certifies that it has reasonable grounds to believe that it meets
all of the requirements for filing on Form S-3 and has duly caused this
Amendment No. 1 to Registration Statement to be signed on its behalf by the
undersigned, thereunto duly authorized, in the City of Boston, Commonwealth of
Massachusetts, on February 9, 2001.

                                          AMERICAN TOWER CORPORATION

                                          By: /s/ Justin D. Benincasa
                                            ----------------------------------

                                            Justin D. Benincasa

                                            Senior Vice President and

                                            Corporate Controller

   Pursuant to the requirements of the Securities Act of 1933, as amended, this
Amendment No. 1 to Registration Statement has been signed by the following
persons in the capacities and on the dates indicated.

             Signatures                         Title                Date

   


                  *                     Chairman, President,     February 9,
-------------------------------------    Chief Executive             2001
           Steven B. Dodge               Officer and
                                         Director (Principal
                                         Executive Officer)

                  *                     Chief Financial          February 9,
-------------------------------------    Officer and                 2001
           Joseph L. Winn                Treasurer
                                         (Principal
                                         Financial and
                                         Accounting Officer)

                  *                     Executive Vice           February 9,
-------------------------------------    President and               2001
             Alan L. Box                 Director

                                        Director
-------------------------------------
          Arnold L. Chavkin

                  *                     Director                 February 9,
-------------------------------------                                2001
          David W. Garrison

                                        Executive Vice
-------------------------------------    President and
       J. Michael Gearon, Jr.            Director

                  *                     Director                 February 9,
-------------------------------------                                2001
           Fred R. Lummis


                                      II-4




                                                         
             Signatures                         Title                Date

                                        Director
               *                                                 February 9,
-------------------------------------                             2001
          Thomas H. Stoner

                                        Director
               *                                                 February 9,
                                                                  2001
-------------------------------------
         Maggie Wilderotter


  *By: /s/ Justin D. Benincasa
-------------------------------------
       Justin D. Benincasa,
         Attorney-in-fact




                                      II-5


                                 EXHIBIT INDEX



 Exhibit
 Number                               Description
 -------                              -----------
      
    4.1   Restated Certificate of Incorporation, as amended, of the Company as
          filed with the Secretary of State of the State of Delaware on June
          4, 1999 (incorporated by reference to Exhibit 3(i) from the
          Registrant's Quarterly Report of Form 10-Q (File No. 001-14195)
          filed on August 16, 1999).
    4.2   By-laws, as amended, of the Registrant (incorporated by reference to
          Exhibit 3.2 from the Registrant's Registration Statement on Form S-3
          (File No. 333-37988) filed on May 26, 2000).
    5.1   Opinion of Hale and Dorr LLP.
  *23.1   Consent of Deloitte & Touche LLP.
  *23.2   Consent of KPMG LLP.
  *23.3   Consent of KPMG LLP.
   23.4   Consent of Hale and Dorr LLP, included in Exhibit 5.1 filed
          herewith.

--------

*  Previously filed.